2026 Pond Symposium Posters

In August of 2025, the South Washington Watershed District (SWWD) began a pilot project to harvest cattails from a large wetland complex in Oakdale, MN. The goal was to learn if that effort could be scaled up to meaningfully and cost-effectively improve water quality in Armstrong Lake. With guidance provided by Barr Engineering Co., SWWD staff led the project with field labor provided by the Washington Conservation District.

This poster summarized work completed, lab analysis conducted, and resulting data, including some interesting local results related to phosphorus and chloride content in cattail biomass. Additional field work and lab analyses are ongoing this winter as well, with results expected in time to be included in the poster. This poster shares our experiences and explore concepts related to management of the harvested cattail material and extrapolate cost-benefit relationships for this work in an effort to continue dialogue on this topic.

Poster file for “Harvesting Cattail Biomass for Water Quality Improvement in Armstrong Lake” [JPG]

Poster description for “Harvesting Cattail Biomass for Water Quality Improvement in Armstrong Lake: A Pilot Study”

Is your pond a Stormwater pond that was specifically designed to treat stormwater, or is it a natural waterbody that receives stormwater?  Understanding the history of pond creation, waterbody modification, eras of development and rules surrounding the NPDES/MS4 and Wetland Conservation Act (WCA) can help! 

Poster file for “What kind of pond do I have?” [JPG]

Poster description for “What kind of pond do I have?”

Utilizing duckweed harvest techniques as a nutrient management tool for stormwater ponds. The City of Bloomington, in collaboration with the University of Minnesota, has undertaken several duckweed harvest trials. These experiments have provided insights into the outcomes of duckweed harvest on pond function but also the cost benefit of harvest as a fiscally sustainable management technique.

Poster file for “Duckweed Harvest: Utilizing floating aquatic plants for nutrient management and pond maintenance” [JPG]

Poster description for “Duckweed Harvest: Utilizing floating aquatic plants for nutrient management and pond maintenance”

Phosphorus is the limiting nutrient in freshwater bodies. When phosphorus is added to a water body it will cause algae blooms, resulting in blue green algae which can release toxic chemicals. Roughly 40% of the lakes across the US are impaired due to excess phosphorus and the resulting eutrophication. We discovered in 2016 that stormwater ponds are not well-mixed, but are stratified due to the high level of sheltering from the wind. The result is that many ponds have low dissolved oxygen levels near the bottom, with internal phosphorus loading from the sediments. We are now working on remediation technologies for ponds that have high internal phosphorus loading to avoid phosphorus export to receiving water bodies.

Poster file for “Research on Pond Remediation Technology” [JPG]

Poster description for “Research on Pond Remediation Technology”

In this project, we combined valuable water quality monitoring resources from 91 sites across the Twin Cities metro area (representing 650+ site-years and the efforts of 12 organizations) into a single database. We used the power of the combined datasets and geospatial indicators to provide a greater understanding of the landscape factors that influence runoff-driven pollutant inputs to surface waters (including ponds) across the metro.

Poster file for “Leveraging Minnesota’s Stormwater Data For Improved Management of Water Quality in Urban Ponds, Lakes, and Streams” [JPG]

Poster description for “Leveraging Minnesota’s Stormwater Data For Improved Management of Water Quality in Urban Ponds, Lakes, and Streams”

Stormwater ponds are a primary best management practice for nutrient and sediment reduction across urban watersheds, yet many experience declining performance over time due to vegetation overgrowth, sediment accumulation, and/or internal nutrient cycling. This poster presents results from 2025 performance monitoring of the Epiphany Creek stormwater pond, a shallow, flow-through system within the Coon Creek Watershed District. Monitoring included water quality samples, continuous water level, vertical sonde profiles, and continuous epilimnion and hypolimnion temperatures. Despite its shallow depth (~1 m), results indicate the pond is experiencing seasonal thermal and dissolved oxygen stratification and periods of phosphorus release, potentially influenced by dense aquatic vegetation. These findings highlight opportunities for applied research on how vegetation management could influence pond mixing and nutrient cycling to improve phosphorus capture. They also underscore challenges commonly faced by aging stormwater ponds and the need for ongoing management and maintenance.

Poster file for “Performance monitoring of a shallow flow-through stormwater pond: epiphany Creek Pond” [JPG]

Poster description for “Performance monitoring of a shallow flow-through stormwater pond: Epiphany Creek Pond”

We developed a spreadsheet-based Pond Assessment Tool which uses readily-available pond characteristics, water quality, and spatial data to provide a low-cost method to assess the risk of and predict phosphorus concentration, sediment phosphate release, and anoxia in ponds treating stormwater. The Tool was built on the results of several years of intensive data collection on water and sediment chemistry from over 35 ponds, enhanced by geospatial data, to develop risk indicators related to pond morphology, floating vegetation, and sediment phosphorus pool that were found to be strongly associated with pond phosphorus performance. The Pond Assessment Tool was developed for stormwater practitioners to conduct assessment of many ponds quickly in an efficient and cost-effective manner, with results intended to inform monitoring or maintenance strategies for pond phosphorus management.

Poster file for “A Stormwater Pond Assessment Tool: Determining Risk of Poor Phosphorus Retention in Stormwater Ponds” [JPG]

Poster description for “A Stormwater Pond Assessment Tool: Determining Risk of Poor Phosphorus Retention in Stormwater Ponds”

Stormwater ponds across a wide variety of characteristics (i.e., watershed history, age, size, depth, aquatic vegetation) are used to treat runoff to remove a significant portion of sediment and associated pollutants such as phosphorus (P). Our field and lab-scale studies on ponds started in 2016. Many pond and landscape features directly or indirectly drive P cycling mechanisms and thus P retention in ponds. The main risk indicators are strongly associated with pond P concentrations, pond anoxia, and sediment P release. These indicators are related to basic pond characteristics or are parameters derived from field, lab and spatial data analysis.

Poster file for “Are Ponds Serving Their Water Quality Function? An overview of the research need, methods, and results of pond assessment” [JPG]

Poster description for “Are Ponds Serving Their Water Quality Function? An overview of the research need, methods, and results of pond assessment” [link]

We are investigating contamination levels in stormwater ponds across the Minneapolis-Saint Paul Metropolitan area to understand how and where ponds accumulate pollutants like heavy metals and microplastics. In this poster, we present research on lead concentrations in pond sediments and water. In particular, we found that older neighborhoods tended to have higher lead in pond sediments, with concentrations increasing deeper in the sediment layers. Importantly, despite elevated lead in some sediments, pond water itself contained relatively little dissolved lead, suggesting that stormwater ponds effectively trap and hold lead within the sediment rather than releasing it downstream. We also present nascent work documenting relative differences in microplastic and PFAS concentrations within the water and sediments of these urban stormwater ponds.

Poster file for “Using Stormwater Ponds to Document the Transport of Urban Contaminants of Concern” [JPG]

Poster description for “Using Stormwater Ponds to Document the Transport of Urban Contaminants of Concern” [link]

Ponds are increasingly recognized as disproportionately large contributors to global greenhouse gas emissions, notably releasing large amounts of methane (CH₄) relative to their surface area. Although previous research has identified broad-scale correlates of pond CH₄ emissions, extreme variability remains in emissions estimates. While the biogeochemical processes controlling CH₄ pathways are well established, most studies have not explicitly applied a process-based framework when investigating the drivers of CH₄ emissions in ponds, and the mechanisms underlying the variability in emissions remain poorly constrained. In this study, we measured CH₄ dynamics and emissions from 15 ponds across New York State (USA). We used an isotopic mass-balance approach to quantify CH₄ oxidation rates and partition total CH₄ production into its major pathways: storage, oxidation, and emissions. This framework allowed us to identify the environmental and biogeochemical drivers underlying each process. Through this mechanistic approach, our study clarifies how interactions among production, storage, and oxidation shape CH₄ emission patterns in ponds.

Poster file for “The Fate of Methane in Ponds: Drivers of Production, Oxidation, and Emissions” [JPG]

Poster description for “The Fate of Methane in Ponds: Drivers of Production, Oxidation, and Emissions” [link]

Beyond flood control, urban stormwater ponds are designed to capture and retain sediment, nutrients, and other pollutants. Sedimentation rates vary between ponds both across the landscape and through time as contributing areas are impacted by construction and development. Therefore, close monitoring and adequate maintenance are critical to successful stormwater management. Bathymetric surveys are an effective way to monitor sediment accumulation over time. Sediment accumulation is the primary driver of maintenance for stormwater ponds, since the storage capacity is what allows ponds to provide volume, rate, and water quality treatment. This poster shares the methods and results for bathymetric surveys of city-owned stormwater ponds conducted during the summer and fall of 2025.   

Poster file for “Mapping Sediment to Plan Smarter: A Practical Bathymetric Survey Approach for Urban Stormwater Ponds” [JPG]

Poster description for “Mapping Sediment to Plan Smarter: A Practical Bathymetric Survey Approach for Urban Stormwater Ponds” [link]

Stormwater ponds provide runoff storage and flood control and water quality benefits. They allow time for solids to settle out and they remove phosphorus from stormwater. Dredging reduces sediment phosphorus concentrations. Dredging also often reduces release of phosphorus from the sediment under anoxic conditions and total phosphorus (TP) concentrations in field water quality.

Poster file for “Dredging Impacts on Phosphorus Release from Stormwater Ponds” [JPG]

Poster description for “Dredging Impacts on Phosphorus Release from Stormwater Ponds” [link]

Sedimentation ponds that accumulate particles and phosphorus from stormwater runoff are a standard, widely applied best management practice. However, aging ponds have potential to release more phosphorus than is captured during summer months. Dredging is an expensive option to improve pond performance, while areal applications of alum and iron can control phosphorus release but incur raw material production and delivery costs. Three years ago, we demonstrated the use of spent lime as a viable alternative for controlling the internal phosphorus load in two stormwater ponds, while also presenting it as an opportunity to provide beneficial re-use for a waste material that is generated by countless drinking water treatment facilities. Factoring in the spent lime disposal costs further confirms that there is significant financial incentive for water utilities to find alternatives for beneficial reuse. Since that time, we have expanded the scope and scale of spent lime applications to control sediment phosphorus release in more, larger water bodies, while continuing to monitor and evaluate the water quality benefits. This presentation discusses the feasibility of spent lime applications to more ponds and longer-term monitoring to evaluate the cost-benefit of areal application and further address proof of concept and permitting issues.

Poster file for “Update on Spent Lime to Control Sediment Phosphorus Release” [JPG]

Poster description for “Update on Spent Lime to Control Sediment Phosphorus Release”

Stormwater ponds across a wide variety of characteristics (i.e., watershed history, age, size, depth, aquatic vegetation) are used to treat runoff to remove a significant portion of sediment and associated pollutants such as phosphorus (P). Our field and lab-scale studies on ponds started in 2016. Many pond and landscape features directly or indirectly drive P cycling mechanisms and thus P retention in ponds. The main risk indicators are strongly associated with pond P concentrations, pond anoxia, and sediment P release. These indicators are related to basic pond characteristics or are parameters derived from field, lab and spatial data analysis.

Poster file for “Are Ponds Serving Their Water Quality Function? An overview of the research need, methods, and results of pond assessment” [JPG]

Poster description for “Are Ponds Serving Their Water Quality Function? An overview of the research need, methods, and results of pond assessment” 

We are investigating contamination levels in stormwater ponds across the Minneapolis-Saint Paul Metropolitan area to understand how and where ponds accumulate pollutants like heavy metals and microplastics. In this poster, we present research on lead concentrations in pond sediments and water. In particular, we found that older neighborhoods tended to have higher lead in pond sediments, with concentrations increasing deeper in the sediment layers. Importantly, despite elevated lead in some sediments, pond water itself contained relatively little dissolved lead, suggesting that stormwater ponds effectively trap and hold lead within the sediment rather than releasing it downstream. We also present nascent work documenting relative differences in microplastic and PFAS concentrations within the water and sediments of these urban stormwater ponds.

Poster file for “Using Stormwater Ponds to Document the Transport of Urban Contaminants of Concern” [JPG]

Poster description for “Using Stormwater Ponds to Document the Transport of Urban Contaminants of Concern” 

Ponds are increasingly recognized as disproportionately large contributors to global greenhouse gas emissions, notably releasing large amounts of methane (CH₄) relative to their surface area. Although previous research has identified broad-scale correlates of pond CH₄ emissions, extreme variability remains in emissions estimates. While the biogeochemical processes controlling CH₄ pathways are well established, most studies have not explicitly applied a process-based framework when investigating the drivers of CH₄ emissions in ponds, and the mechanisms underlying the variability in emissions remain poorly constrained. In this study, we measured CH₄ dynamics and emissions from 15 ponds across New York State (USA). We used an isotopic mass-balance approach to quantify CH₄ oxidation rates and partition total CH₄ production into its major pathways: storage, oxidation, and emissions. This framework allowed us to identify the environmental and biogeochemical drivers underlying each process. Through this mechanistic approach, our study clarifies how interactions among production, storage, and oxidation shape CH₄ emission patterns in ponds.

Poster file for “The Fate of Methane in Ponds: Drivers of Production, Oxidation, and Emissions” [JPG]

Poster description for “The Fate of Methane in Ponds: Drivers of Production, Oxidation, and Emissions” 

Beyond flood control, urban stormwater ponds are designed to capture and retain sediment, nutrients, and other pollutants. Sedimentation rates vary between ponds both across the landscape and through time as contributing areas are impacted by construction and development. Therefore, close monitoring and adequate maintenance are critical to successful stormwater management. Bathymetric surveys are an effective way to monitor sediment accumulation over time. Sediment accumulation is the primary driver of maintenance for stormwater ponds, since the storage capacity is what allows ponds to provide volume, rate, and water quality treatment. This poster shares the methods and results for bathymetric surveys of city-owned stormwater ponds conducted during the summer and fall of 2025.   

Poster file for “Mapping Sediment to Plan Smarter: A Practical Bathymetric Survey Approach for Urban Stormwater Ponds” [JPG]

Poster description for “Mapping Sediment to Plan Smarter: A Practical Bathymetric Survey Approach for Urban Stormwater Ponds”

Stormwater ponds provide runoff storage and flood control and water quality benefits. They allow time for solids to settle out and they remove phosphorus from stormwater. Dredging reduces sediment phosphorus concentrations. Dredging also often reduces release of phosphorus from the sediment under anoxic conditions and total phosphorus (TP) concentrations in field water quality.

Poster file for “Dredging Impacts on Phosphorus Release from Stormwater Ponds” [JPG]

Poster description for “Dredging Impacts on Phosphorus Release from Stormwater Ponds”